- 你赞同Bayesian理论吗？
击打快速运动的网球是一项复杂的任务。一方面很难追踪球的运动轨迹，另一方面我们的视觉会提供网球弹跳落点不准确的信息。根据视觉上的输入，一个网球运动员能判断不同弹跳落点的可能性（封面上的红色部分）。从理论上讲，通过利用较长时间段内获取的信息有可能提高这种判断力：因为所有落点的可能性并不均等。在比赛中，这些可能的落点必将有一个概率分布区（绿色部分）。Bayesian理论告诉我们：通过综合落点概率和视觉上的判断，我们可以得到关于落点或边线最优的判断。在这个关于打网球的抽象事件中，Kording和Wolpert提供了一个实验对象按照Bayesian过程，掌握落点分布理论，并整合视觉输入的证据。 - Bayesian integration in sensorimotor learning
- When we learn a new motor skill, such as playing an approaching tennis ball, both our sensors and the task possess variability. Our sensors provide imperfect information about the ball's velocity, so we can only estimate it. Combining information from multiple modalities can reduce the error in this estimate. On a longer time scale, not all velocities are a priori equally probable, and over the course of a match there will be a probability distribution of velocities. According to bayesian theory, an optimal estimate results from combining information about the distribution of velocities—the prior—with evidence from sensory feedback. As uncertainty increases, when playing in fog or at dusk, the system should increasingly rely on prior knowledge. To use a bayesian strategy, the brain would need to represent the prior distribution and the level of uncertainty in the sensory feedback. Here we control the statistical variations of a new sensorimotor task and manipulate the uncertainty of the sensory feedback. We show that subjects internally represent both the statistical distribution of the task and their sensory uncertainty, combining them in a manner consistent with a performance-optimizing bayesian process. The central nervous system therefore employs probabilistic models during sensorimotor learning.
动物学家用于生命分类的许多标准多是基于那些几乎不可能成为化石的特征，比如成年动物是否直接从受精卵发育而来，或者最后成体完全不同的幼体发育是否要经历一个变态过程。“胚胎”化石记录的慢慢积累将有助于填补这一缺口。在化石形成发生之前，柔软的胚胎组织通常就已经消失了，但是生活在5亿年前的一种被叫做“Markuelia”的蠕虫样动物的一系列细小胚胎化石的发现，为我们提供了反映寒武纪生命历史细节的物质证据。重要的是，这些微小化石还显示，成体Markuelia直接从蠕虫样的卵发育而来。这一点和许多Markuelia的现代近亲不同。这揭示Markuelia种群的发育在最初是简单、直接的。
- 机器人博士
在科学的许多领域，数据的产生往往比对数据的有效分析要快。因此，科学活动能否实现自动化这一问题就不仅仅只是理论上的兴趣了。King等人作了一个标准验证实验，显示机器人科学家是个现实的概念，至少在功能基因组研究中应该如此。通过使用人工智能研究中的教训制造出机器人，它能够自动地创造事实假设来解释数据，修正实验以验证其假设，并且能指导实验室的机器人完成试验。然后它还能对实验结果作出评估，并且如果需要它还继续进行更多的实验。这个机器人的第一个工作是使用酵母缺失突变和生长实验来研究基因功能。 - Functional genomic hypothesis generation and experimentation by a robot scientist
- The question of whether it is possible to automate the scientific process is of both great theoretical interest and increasing practical importance because, in many scientific areas, data are being generated much faster than they can be effectively analysed. We describe a physically implemented robotic system that applies techniques from artificial intelligence to carry out cycles of scientific experimentation. The system automatically originates hypotheses to explain observations, devises experiments to test these hypotheses, physically runs the experiments using a laboratory robot, interprets the results to falsify hypotheses inconsistent with the data, and then repeats the cycle. Here we apply the system to the determination of gene function using deletion mutants of yeast (Saccharomyces cerevisiae) and auxotrophic growth experiments. We built and tested a detailed logical model (involving genes, proteins and metabolites) of the aromatic amino acid synthesis pathway. In biological experiments that automatically reconstruct parts of this model, we show that an intelligent experiment selection strategy is competitive with human performance and significantly outperforms, with a cost decrease of 3-fold and 100-fold (respectively), both cheapest and random-experiment selection.
- 异硫氰酸酯
芥末类厨房调味品，如辣根、山萸菜（来源于草本植物Eutrema wasabi的根，在日本烹饪中常见）为什么能产生我们熟悉的辛辣气味，其分子机制已经被解开。它们的活性成分为异硫氰酸酯和烯丙基异硫氰酸酯（即芥末油），我们已经知道当把它们使用到皮肤上时，它们能激活感觉神经末梢并导致痛觉。异硫氰酸酯敏感的感觉神经元亚类现在已经被发现。被称为ANKTM1的受体是TRP离子通道家族的一个成员，这一受体在最近有害寒气的检测中被发现。红辣椒含有能与不同受体结合的不同活性成分（即辣椒素）。有趣的是，四氢大麻酚既能激活山萸菜的受体类型，又能激活红辣椒的受体类型。 - Mustard oils and cannabinoids excite sensory nerve fibres through the TRP channel ANKTM1
- Wasabi, horseradish and mustard owe their pungency to isothiocyanate compounds. Topical application of mustard oil (allyl isothiocyanate) to the skin activates underlying sensory nerve endings, thereby producing pain, inflammation and robust hypersensitivity to thermal and mechanical stimuli. Despite their widespread use in both the kitchen and the laboratory, the molecular mechanism through which isothiocyanates mediate their effects remains unknown. Here we show that mustard oil depolarizes a subpopulation of primary sensory neurons that are also activated by capsaicin, the pungent ingredient in chilli peppers, and by
9-tetrahydrocannabinol (THC), the psychoactive component of marijuana. Both allyl isothiocyanate and THC mediate their excitatory effects by activating ANKTM1, a member of the TRP ion channel family recently implicated in the detection of noxious cold. These findings identify a cellular and molecular target for the pungent action of mustard oils and support an emerging role for TRP channels as ionotropic cannabinoid receptors.
- X-射线双星Circinus X-1
Circinus X-1是一个X-射线双星体系，含有一个正常的恒星和一个中子星，前者与我们的太阳差不多。中子星的引力将物质从其伴星那里拉过来，形成一个增长盘。此外，Circinus X-1是具有从中子星流出的高速物质喷射流的少数几个已知X-射线双星之一。新的观测显示，Circinus X-1双星中来自该中子星的外流喷射流的速度是超相对论的，可与来自“活动星系核”（AGN）的最快的外流喷射流相比。这说明，高度相对论的外流喷射流并不要求黑洞所特有的性质，而黑洞则被认为是驱动AGN的能量来源。 - An ultra-relativistic outflow from a neutron star accreting gas from a companion
- Collimated relativistic outflows—also known as jets—are amongst the most energetic phenomena in the Universe. They are associated with supermassive black holes in distant active galactic nuclei, accreting stellar-mass black holes and neutron stars in binary systems and are believed to be responsible for
-ray bursts. The physics of these jets, however, remains something of a mystery in that their bulk velocities, compositions and energetics remain poorly determined. Here we report the discovery of an ultra-relativistic outflow from a neutron star accreting gas within a binary stellar system. The velocity of the outflow is comparable to the fastest-moving flows observed from active galactic nuclei, and its strength is modulated by the rate of accretion of material onto the neutron star. Shocks are energized further downstream in the flow, which are themselves moving at mildly relativistic bulk velocities and are the sites of the observed synchrotron emission from the jet. We conclude that the generation of highly relativistic outflows does not require properties that are unique to black holes, such as an event horizon.
- 超级固体氦终于被发现
超级固体氦是一种难以捉摸的物质形式，具有几乎无法置信、却又被理论工作者明确预测出的性质。现在看来，这种物质形式似乎终于被发现了。冷却到2.172K的液态氦-4变成一种“超级流体”，即一种零粘度的流体，可通过甚至原子尺度的小孔流动。一种“超级流体”具有“超级流动”的能力似乎是自然的，但理论预测，“超级流动”甚至可在氦的固体相中出现。试图在大体积固体氦中观察这一现象的很多尝试都失败了。但是现在，科学家们已在高压下在固体氦中观察到了存在“超级流动性”的证据。他们是在一种被称为Vycor的固体盘中观察到这一现象的，Vycor是一种96%的硅酸盐玻璃，更多地用于高温应用场合。固体氦之所以具有这种本领，是因为它们在晶体状固体中存在移位的空穴和缺陷，这些空穴和缺陷是由量子力学波动造成的。 - Probable observation of a supersolid helium phase
- When liquid 4He is cooled below 2.176 K, it undergoes a phase transition—Bose–Einstein condensation—and becomes a superfluid with zero viscosity. Once in such a state, it can flow without dissipation even through pores of atomic dimensions. Although it is intuitive to associate superflow only with the liquid phase, it has been proposed theoretically that superflow can also occur in the solid phase of 4He. Owing to quantum mechanical fluctuations, delocalized vacancies and defects are expected to be present in crystalline solid 4He, even in the limit of zero temperature. These zero-point vacancies can in principle allow the appearance of superfluidity in the solid. However, in spite of many attempts, such a 'supersolid' phase has yet to be observed in bulk solid 4He. Here we report torsional oscillator measurements on solid helium confined in a porous medium, a configuration that is likely to be more heavily populated with vacancies than bulk helium. We find an abrupt drop in the rotational inertia of the confined solid below a certain critical temperature. The most likely interpretation of the inertia drop is entry into the supersolid phase. If confirmed, our results show that all three states of matter—gas, liquid and solid—can undergo Bose–Einstein condensation.
- 间接气溶胶效应对气候的影响
由人类活动产生的气溶胶（空气中微小的颗粒状污染物，是烟雾污染的主要成分）可通过增加云中液滴的数量浓度来增强云的反射率。很多小液滴与较少的大液滴相比，可将更多阳光反射进太空，所以理论上气溶胶颗粒的积聚可产生变冷效应，被称为“间接气溶胶效应”。“政府间气候变化小组”（IPCC）曾经得出结论认为，气溶胶的间接效应也许是可以忽略的，部分是由于缺乏这种机制影响进入云层的太阳辐射和流出云层的红外辐射之间平衡的直接证据。来自被污染地点（美国俄克拉荷马）和干净地点（美国阿拉斯加）的空气的新数据表明，气溶胶污染物显著影响云的光学深度，其影响的程度与从间接气溶胶效应预计出的程度相同，所以间接气溶胶效应对气候有重要影响。 - Observational evidence of a change in radiative forcing due to the indirect aerosol effect
- Anthropogenic aerosols enhance cloud reflectivity by increasing the number concentration of cloud droplets, leading to a cooling effect on climate known as the indirect aerosol effect. Observational support for this effect is based mainly on evidence that aerosol number concentrations are connected with droplet concentrations, but it has been difficult to determine the impact of these indirect effects on radiative forcing. Here we provide observational evidence for a substantial alteration of radiative fluxes due to the indirect aerosol effect. We examine the effect of aerosols on cloud optical properties using measurements of aerosol and cloud properties at two North American sites that span polluted and clean conditions—a continental site in Oklahoma with high aerosol concentrations, and an Arctic site in Alaska with low aerosol concentrations. We determine the cloud optical depth required to fit the observed shortwave downward surface radiation. We then use a cloud parcel model to simulate the cloud optical depth from observed aerosol properties due to the indirect aerosol effect. From the good agreement between the simulated indirect aerosol effect and observed surface radiation, we conclude that the indirect aerosol effect has a significant influence on radiative fluxes.
- 外部因素对湖泊生态系统的影响
支持湖泊和池塘中食物链的有机物和能量的主要来源是通过本地光合作用进行的内部初级生产。或者，这种观点至少是生态学教科书中的共同假设。最近的证据表明，外部补充在维持这些生态系统运转中起着较大作用，新的整生态系统实验对这一不同观点提供了支持。密歇根两个湖泊中的内部初级生产不足以支持这些生态系统。碳同位素动态表明，来自溶解的物质和颗粒状物质的陆地碳来源对水生食物链有显著贡献，浮游动物多达50%的碳来自陆地来源。这些结果说明，有机碳的流域输入将陆地生态系统与水生食物链联系起来，不仅支持细菌，而且支持无脊椎动物和鱼类。 - Whole-lake carbon-13 additions reveal terrestrial support of aquatic food websEcosystems are supported by organic carbon from two distinct sources. Endogenous carbon is produced by photosynthesis within an ecosystem by autotrophic organisms. Exogenous carbon is produced elsewhere and transported into ecosystems. Consumers may use exogenous carbon with consequent influences on population dynamics, predator–prey relationships and ecosystem processes. For example, exogenous inputs provide resources that may enhance consumer abundance beyond levels supported by within-system primary production. Exogenous fluxes of organic carbon to ecosystems are often large, but this material is recalcitrant and difficult to assimilate, in contrast to endogenously produced organic matter, which is used more easily. Here we show, by the experimental manipulation of dissolved inorganic 13C in two lakes, that internal primary production is insufficient to support the food webs of these ecosystems. Additions of NaH13CO3 enriched the 13C content of dissolved inorganic carbon, particulate organic carbon, zooplankton and fish. Dynamics of 13C indicate that 40–55% of particulate organic carbon and 22–50% of zooplankton carbon are derived from terrestrial sources, showing that there is significant subsidy of these ecosystems by organic carbon produced outside their boundaries.
